Manganese oxide-coated oyster shell for heavy metal immobilization in contaminated soils

Abstract This study investigates the potential of modified oyster shells (OS) as an effective adsorbent for immobilizing copper (Cu) and cadmium (Cd) in contaminated soils. Given the rising concerns regarding heavy metal pollution from both natural and anthropogenic sources, innovative solutions for remediation are essential. The research focuses on enhancing granular OS (GOS) through a dual modification process involving NaOH treatment and subsequent coating with manganese oxide (MnO x ) using potassium permanganate (KMnO 4 ). Batch adsorption experiments revealed that MnO x -coated GOS (MnO x @GOS) exhibited superior adsorption capacities for Cu²⁺ (0.83 mg g⁻¹) and Cd²⁺ (0.76 mg g⁻¹), fitting the pseudo-second-order kinetic model. In soil column experiments, MnO x @GOS achieved removal efficiencies exceeding 99% for Cu²⁺ and 65% for Cd²⁺ over 180 h. Soil incubation experiments demonstrated that MnO x @GOS reduced pore water concentrations of Cu and Cd by 82 and 77%, respectively, compared to the control. When applied to actual contaminated soil, MnO x @GOS achieved over 96% immobilization efficiency for Cd and Zn and 52% for Cu compared to the control group. This research not only addresses the environmental challenge posed by heavy metal contamination but also promotes the recycling of waste OS, providing a sustainable approach to soil remediation.